Conventional solar power systems utilizing optical fibers generally employ a single large lens (or mirror). An orientation system causes the lens to face the sun. The lens causes a solar image to be focused upon the open end of a bundle of optical fibers. For a typical system see Dismer, U.S. Pat. No. 4,201,197. The bundle is led into a building where the radiation is delivered to a receiver. In a variation of this system (Coleman, U.S. Pat. No. 4,023,267) a mosaic of lenses is provided. Each lens focuses a solar image upon the open end of a respective bundle of fibers. The result is a collector of far less bulk--a collector which may be fitted into a flat plate and neatly affixed to the roof.
A typical solar collector used to supply energy to homes generally has a diameter of 2 meters. EQU D=2 m 1.
Since the conventional optical fiber will accept radiation striking the fiber at an angle 30.degree. off axis, the minimum focal length becomes ##EQU1## The sun subtends an angle of approximately 0.01 radians. Consequently the diameter of the solar image is given by ##EQU2## The largest commercially available optical fiber is 1 mm in diameter. Consequently the number of fibers which must be carried in a bundle the end of which will encompass the solar image is EQU N=(DI/DO).sup.2 4.
where
DI is the diameter of the solar image. PA1 DF is the diameter of the fiber. Substituting in 4 EQU N=(17.3).sup.2 =300 5. PA1 1. The front surface of the lens. PA1 2. The rear surface of the lens. PA1 3. The inlet end of the fiber. PA1 4. The outlet end of the fiber.
The above figure would be correct were there no interstitial space between fibers. The interstitial space reduces the number of fibers required by 10%. However, a perfect solar image will never be obtained. Imperfection in the image will cause the number of fibers to be greater. The two errors tend to compensate each other. The figure obtained above appears sufficient for our purposes.
In the system of Coleman a matrix of lenses each estimated to be 600 mm in diameter is used. The resultant focal length becomes ##EQU3## The diameter of the solar image becomes EQU ID=0.01 FL=5.2 mm 6.
The consequent number of fibers required in the bundle becomes ##EQU4## While the system of Coleman is an improvement over the system of Dismer in that the bulk of the collector system has been reduced, the loss associated with the interstitial space remains undiminished.
Reflection losses plague optical systems such as that under discussion. Each refracting surface reflects approximately 10%. A conventional system gives reflections at
The 10% loss at each surface causes a total loss of 35%. Consequently it is desirable to eliminate as many of the above reflecting surfaces as possible.